Heavy hydrides: H2Te ultraviolet photochemistry

The room-temperature ultraviolet absorption spectrum of H2Te has been recorded. Unlike other group-6 hydrides, it displays a long-wavelength tail that extends to 400 nm. Dissociation dynamics have been examined at photolysis wavelengths of 266 nm (which lies in the main absorption feature) and 355 nm (which lies in the long-wavelength tail) by using high-n Rydberg time-of-flight spectroscopy to obtain center-of-mass translational energy distributions for the channels that yield H atoms. Photodissociation at 355 nm yields TeH(2Pi1/2) selectively relative to the TeH(2Pi3/2) ground state. This is attributed to the role of the 3A' state, which has a shallow well at large R(H-TeH) and correlates to H+TeH(2Pi1/2). Note that the 2Pi1/2 state is analogous to the 2P1/2 spin-orbit excited state of atomic iodine, which is isoelectronic with TeH. The 3A' state is crossed at large R only by 2A", with which it does not interact. The character of 3A' at large R is influenced by a strong spin-orbit interaction in the TeH product. Namely, 2Pi1/2 has a higher degree of spherical symmetry than does 2Pi3/2 (recall that I(2P1/2) is spherically symmetric), and consequently 2Pi1/2 is not inclined to form either strongly bonding or antibonding orbitals with the H atom. The 3A'<--X transition dipole moment dominates in the long-wavelength region and increases with R. Structure observed in the absorption spectrum in the 380-400 nm region is attributed to vibrations on 3A'. The main absorption feature that is peaked at approximately 240 nm might arise from several excited surfaces. On the basis of the high degree of laboratory system spatial anisotropy of the fragments from 266 nm photolysis, as well as high-level theoretical studies, the main contribution is believed to be due to the 4A" surface. The 4A"<--X transition dipole moment dominates in the Franck-Condon region, and its polarization is in accord with the experimental observations. An extensive secondary photolysis (i.e., of nascent TeH) is observed at 266 and 355 nm, and the corresponding spectral features are assigned. Analyses of the c.m. translational energy distributions yield bond dissociation energies D0. For H2Te and TeH, these are 65.0+/-0.1 and 63.8+/-0.4 kcalmol, respectively, in good agreement with predictions that use high-level relativistic theory.     

A microfabricated capillary electrophoresis chip with multiple buried optical fibers and microfocusing lens for multiwavelength detection

We present a new microfluidic device utilizing multiwavelength detection for high-throughput capillary electrophoresis (CE). In general, different fluorescent dyes are only excited by light sources with appropriate wavelengths. When excited by an appropriate light source, a fluorescent dye emits specific fluorescence signals of a longer wavelength. This study designs and fabricates plastic micro-CE chips capable of performing multiple-wavelength fluorescence detection by means of multimode optic fiber pairs embedded downstream of the separation channel. For detection purposes, the fluorescence signals are enhanced by positioning microfocusing lens structures at the outlets of the excitation fibers and the inlets of the detection fibers, respectively. The proposed device is capable of detecting multiple samples labeled with different kinds of fluorescent dyes in the same channel in a single run. The experimental results demonstrate that various proteins, including bovine serum albumin and beta-casein, can be successfully injected and detected by coupling two light sources of different wavelengths to the two excitation optic fibers. Furthermore, the proposed device also provides the ability to measure the speed of the samples traveling in the microchannel. The developed multiwavelength micro-CE chip could have significant potential for the analysis of DNA and protein samples.     

A surface plasmon resonance biosensor for detecting Pseudomonas aeruginosa cells with self-assembled chitosan-alginate multilayers

A self-assembled multilayer (SAMu) including the alginate layer was prepared for detecting Pseudomonas aeruginosa cells in a solution and its potential was evaluated with a BIAcore system. After layer-by-layer formation, the refractive units (RU) values monitored with the biosensor increased by the interaction between the layers. The responses by the binding of P. aeruginosa cells to the alginate-immobilized SAMu were visualized immediately upon injection of the cell suspension. The RU values after injection of the cells were measured with approximately 1152, 656 and 173 for 1 × 10⁹, 1 × 10⁸ and 1 × 10⁷ CFU/ml. This result suggests that the alginate-immobilized SAMu will have useful application for detecting P. aeruginosa cells in a biosensor analysis.     

Synthesis of the apoptosis inducing agent apoptolidin. Assembly of the C(16)-C(28) fragment

[reaction--see text] A stereoselective synthesis of the C(16)-C(28) fragment of the apoptosis inducing agent apoptolidin is described. Key steps include two propionate aldol reactions and a stereoselective Mukaiyama aldol addition of enolsilane 19 to beta-methoxy aldehyde 4.     

Electrophoretic characterization of a novel cysteine protease produced by Vibrio harveyi

Electrophoretic characterization of a novel cysteine protease produced by pathogenic luminous Vibrio harveyi, originally isolated from diseased tiger prawn Penaeus monodon in Taiwan, is demonstrated in the present study using native polyacrylamide gel electrophoresis (native PAGE), sodium dodecyl sulfate-PAGE (SDS-PAGE), crossed immunoelectrophoresis (CIE) and isoelectric focusing (IEF) gels. The protease has a pI of 6.4 and exhibits a fast-migrating feature in native-PAGE and CIE gels indicating that it is a negatively charged protease. The protease electrophoresed as a 22 kDa protein band in native- and SDS-PAGE (in SDS - buffer with or without the presence of 2-mercaptoethanol) while it electrophoresed as a 38 kDa protein band in SDS-PAGE when the samples were boiled for 10 min prior to electrophoresis. The results reveal that the enzyme is an SDS-resistant monomeric protease and its high negative charge is not influenced by SDS (detergent) without boiling the sample. The present results are useful in determining proteins of similar nature to this unique cysteine protease.     

Ab initio and DFT studies on hydrolyses of phosphorus halides

Hydrolyses of phosphorus halides, (RO)(2)POX where R = H or Me and X = F or Cl, in the gas phase and in the reaction field have been investigated theoretically with ab initio and the density functional theory (DFT). The free energy of activation in the reaction field was also estimated using the Onsager method with a correction of entropy change and basis set superposition error (BSSE). The reaction of (MeO)(2)POF proceeds through a path with bifunctional catalysis regardless of the medium, but the reaction of (MeO)(2)POCl proceeds through bifunctional and general base catalysis in the gas phase and in water, respectively. The estimated free energy barrier of 23 kcal/mol for the hydrolysis of (MeO)(2)POF is in good agreement with the experimental values of 24 kcal/mol, and relative barrier of 3 kcal/mol to the (MeO)(2)POCl is also in good agreement with the experimental values of 5 kcal/mol of diisopropyl phosphorus halides ((Pr(i)O)(2)POX, X = F and Cl).     

Low flow high-performance liquid chromatography solvent delivery system designed for tandem capillary liquid chromatography-mass spectrometry

A solvent delivery system is described that is designed to increase the efficiency of liquid chromatography-mass spectrometry (LC/MS) analyses. Gradients formed by using two low pressure syringe pumps are stored in a length of narrow bore tubing (gradient loop) mounted on a standard high pressure switching valve. The preformed gradient is pushed through the column by using a high pressure syringe pump. The system is fully automated and can be controlled with either a personal computer or the mass spectrometer data system. Advantages include gradient operation without the use of split flows, pressure programed flow control for rapid sample loading and recycling to initial conditions, and a flow rate range of 0.1–20 μL/min, which is suitable for packed capillary columns 50–500 μm in diameter. The system has been used extensively for rapid molecular weight determinations of intact protein samples, as well as LC/MS and liquid chromatography-tandem mass spectrometry analyses of complex peptide mixtures.     

Bend intersection property and dendroids of type N

It is proved that a dendroidX is not of typeN if and only if for each arc ofX, the intersection of all its bend sets is nonempty.